1. Technical Field
The present invention relates to integrated circuits in general, and, in particular, to integrated circuit devices having output drivers. Still more particularly, the present invention relates to a method and apparatus for generating impedance matched output signals for an integrated circuit device.
2. Description of the Related Art
The clock rates of modern integrated circuit devices now routinely operate beyond 500 MHz. At such high frequencies, the output ports of an integrated circuit device to which interconnects on a printed circuit board are connected are required to have their impedance matched with the intrinsic impedance of the interconnects in order to minimize signal reflections (or ringing) on the interconnects during data transmissions. Otherwise, the occurrence of signal reflections on interconnects can add delays to the signal transmission time, both at the receiving end of the interconnects and at any intermediate taps along the interconnects.
Since signal reflection errors increase with the operating speed of an integrated circuit device, it becomes even more important to match the impedance of interface circuits, such as output driver circuits, of an ultra-high speed integrated circuit device with the impedances of associated interconnects on a printed circuit board in order to prevent signal reflection errors during the transmission of high-frequency signals. As such, when designing a printed circuit board, discrete impedance matching resistors, which have comparable impedance as the impedance of the interconnects on the printed circuit board, are added between the output driver circuits within the integrated circuit device and the interconnects on the printed circuit board for the purpose of impedance matching. In this way, the impedance of the interface circuits is xe2x80x9cautomaticallyxe2x80x9d matched with the impedances of the interconnects on the printed circuit board, according to the values of the discrete resistors. However, the addition of impedance matching resistors is costly, consumes a relatively large amount of area and may even affect the performance of the interface circuit within the integrated circuit device. As such, it is desirable to provide an improved method for generating impedance matched output signals for an integrated circuit device such that the usage of impedance matching resistors can be minimized.
In accordance with a preferred embodiment of the present invention, an apparatus for generating output signals with impedance matching for an integrated circuit includes a master true driver circuit, a master complement driver circuit and multiple clone output driver circuits. The master true driver circuit includes a first driver control, a first output driver, a first impedance matching resistor and a first load. The master complement driver circuit includes a second driver control, a second output driver, a second impedance matching resistor and a second load. The clone output driver circuits, which are substantially identical to each other, can produce impedance matched output signals to their respective substantially identical loads. Each of the clone output driver circuit includes a driver control, a first unity gain amplifier, a second unity gain amplifier and a load. The inputs to the first and second unity gain amplifiers are supplied by the master true circuit and the master complement circuit via the driver control.
All objects, features, and advantages of the present invention will become apparent in the following detailed written description.